Systems and methods for removing a background of an image

ABSTRACT

An image such as a depth image of a scene may be received, observed, or captured by a device. A grid of voxels may then be generated based on the depth image such that the depth image may be downsampled. A background included in the grid of voxels may then be discarded to isolate one or more voxels associated with a foreground object such as a human target and the isolated voxels associated with the foreground object may be processed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/143,879, filed on Dec. 30, 2013, which is a divisional of U.S. patentapplication Ser. No. 12/575,363, filed on Oct. 7, 2009 (now U.S. Pat.No. 8,867,820 issued Oct. 21, 2014), the contents of each areincorporated herein by reference in their entireties.

BACKGROUND

Many computing applications such as computer games, multimediaapplications, or the like use controls to allow users to manipulate gamecharacters or other aspects of an application. Typically such controlsare input using, for example, controllers, remotes, keyboards, mice, orthe like. Unfortunately, such controls can be difficult to learn, thuscreating a barrier between a user and such games and applications.Furthermore, such controls may be different than actual game actions orother application actions for which the controls are used. For example,a game control that causes a game character to swing a baseball bat maynot correspond to an actual motion of swinging the baseball bat.

SUMMARY

Disclosed herein are systems and methods for tracking a user in a scene.For example, an image such as depth image of a scene may be received orobserved. A grid of voxels may then be generated based on the depthimage such that the depth image may be downsampled. For example, thedepth image may include a plurality of pixels that may be divided intoportions or blocks. A voxel may then be generated for each portion orblock such that the received depth image may be downsampled into thegrid of voxels.

A background of the grid of voxels may be determined and discarded orremoved such that one or more voxels associated with a foreground objectsuch as a human target may be isolated. According to one embodiment, thetarget recognition, analysis, and tracking system may determine thebackground. To determine the background, the target recognition,analysis, and tracking system may determine objects in the grid ofvoxels that may be moving and non-moving. The target recognition,analysis, and tracking system may discard the objects that may benon-moving as background.

The target recognition, analysis, and tracking system may then processthe voxels associated with the human target that may be discarded. Forexample, the target recognition, analysis, and tracking system maydetermine one or more extremities for the isolated human target, maydetermine dimensions of such extremities, may generate a model for theisolated human target, or the like.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate an example embodiment of a targetrecognition, analysis, and tracking system with a user playing a game.

FIG. 2 illustrates an example embodiment of a capture device that may beused in a target recognition, analysis, and tracking system.

FIG. 3 illustrates an example embodiment of a computing environment thatmay be used to interpret one or more gestures in a target recognition,analysis, and tracking system and/or animate an avatar or on-screencharacter displayed by a target recognition, analysis, and trackingsystem.

FIG. 4 illustrates another example embodiment of a computing environmentthat may be used to interpret one or more gestures in a targetrecognition, analysis, and tracking system and/or animate an avatar oron-screen character displayed by a target recognition, analysis, andtracking system.

FIG. 5 depicts a flow diagram of an example method for processing depthinformation of a scene.

FIG. 6 illustrates an example embodiment of a depth image that may becaptured or observed.

FIGS. 7A-7B illustrates an example embodiment of a portion of the depthimage being downsampled.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1A and 1B illustrate an example embodiment of a configuration of atarget recognition, analysis, and tracking system 10 with a user 18playing a boxing game. In an example embodiment, the target recognition,analysis, and tracking system 10 may be used to recognize, analyze,and/or track a human target such as the user 18.

As shown in FIG. 1A, the target recognition, analysis, and trackingsystem 10 may include a computing environment 12. The computingenvironment 12 may be a computer, a gaming system or console, or thelike. According to an example embodiment, the computing environment 12may include hardware components and/or software components such that thecomputing environment 12 may be used to execute applications such asgaming applications, non-gaming applications, or the like. In oneembodiment, the computing environment 12 may include a processor such asa standardized processor, a specialized processor, a microprocessor, orthe like that may execute instructions including, for example,instructions for receiving a depth image; generating a grid of voxelsbased on the depth image; determining whether one or more voxels in thegrid are associated with a background; discarding the one or more voxelsassociated with the background to isolate voxels associated with aforeground object in the depth image; processing the grid with theisolated foreground object, or any other suitable instruction, whichwill be described in more detail below.

As shown in FIG. 1A, the target recognition, analysis, and trackingsystem 10 may further include a capture device 20. The capture device 20may be, for example, a camera that may be used to visually monitor oneor more users, such as the user 18, such that gestures and/or movementsperformed by the one or more users may be captured, analyzed, andtracked to perform one or more controls or actions within an applicationand/or animate an avatar or on-screen character, as will be described inmore detail below.

According to one embodiment, the target recognition, analysis, andtracking system 10 may be connected to an audiovisual device 16 such asa television, a monitor, a high-definition television (HDTV), or thelike that may provide game or application visuals and/or audio to a usersuch as the user 18. For example, the computing environment 12 mayinclude a video adapter such as a graphics card and/or an audio adaptersuch as a sound card that may provide audiovisual signals associatedwith the game application, non-game application, or the like. Theaudiovisual device 16 may receive the audiovisual signals from thecomputing environment 12 and may then output the game or applicationvisuals and/or audio associated with the audiovisual signals to the user18. According to one embodiment, the audiovisual device 16 may beconnected to the computing environment 12 via, for example, an S-Videocable, a coaxial cable, an HDMI cable, a DVI cable, a VGA cable, or thelike.

As shown in FIGS. 1A and 1B, the target recognition, analysis, andtracking system 10 may be used to recognize, analyze, and/or track ahuman target such as the user 18. For example, the user 18 may betracked using the capture device 20 such that the gestures and/ormovements of user 18 may be captured to animate an avatar or on-screencharacter and/or may be interpreted as controls that may be used toaffect the application being executed by computer environment 12. Thus,according to one embodiment, the user 18 may move his or her body tocontrol the application and/or animate the avatar or on-screencharacter.

As shown in FIGS. 1A and 1B, in an example embodiment, the applicationexecuting on the computing environment 12 may be a boxing game that theuser 18 may be playing. For example, the computing environment 12 mayuse the audiovisual device 16 to provide a visual representation of aboxing opponent 38 to the user 18. The computing environment 12 may alsouse the audiovisual device 16 to provide a visual representation of aplayer avatar 40 that the user 18 may control with his or her movements.For example, as shown in FIG. 1B, the user 18 may throw a punch inphysical space to cause the player avatar 40 to throw a punch in gamespace. Thus, according to an example embodiment, the computerenvironment 12 and the capture device 20 of the target recognition,analysis, and tracking system 10 may be used to recognize and analyzethe punch of the user 18 in physical space such that the punch may beinterpreted as a game control of the player avatar 40 in game spaceand/or the motion of the punch may be used to animate the player avatar40 in game space.

Other movements by the user 18 may also be interpreted as other controlsor actions and/or used to animate the player avatar, such as controls tobob, weave, shuffle, block, jab, or throw a variety of different powerpunches. Furthermore, some movements may be interpreted as controls thatmay correspond to actions other than controlling the player avatar 40.For example, in one embodiment, the player may use movements to end,pause, or save a game, select a level, view high scores, communicatewith a friend, etc. According to another embodiment, the player may usemovements to select the game or other application from a main userinterface. Thus, in example embodiments, a full range of motion of theuser 18 may be available, used, and analyzed in any suitable manner tointeract with an application.

In example embodiments, the human target such as the user 18 may have anobject. In such embodiments, the user of an electronic game may beholding the object such that the motions of the player and the objectmay be used to adjust and/or control parameters of the game. Forexample, the motion of a player holding a racket may be tracked andutilized for controlling an on-screen racket in an electronic sportsgame. In another example embodiment, the motion of a player holding anobject may be tracked and utilized for controlling an on-screen weaponin an electronic combat game.

According to other example embodiments, the target recognition,analysis, and tracking system 10 may further be used to interpret targetmovements as operating system and/or application controls that areoutside the realm of games. For example, virtually any controllableaspect of an operating system and/or application may be controlled bymovements of the target such as the user 18.

FIG. 2 illustrates an example embodiment of the capture device 20 thatmay be used in the target recognition, analysis, and tracking system 10.According to an example embodiment, the capture device 20 may beconfigured to capture video with depth information including a depthimage that may include depth values via any suitable techniqueincluding, for example, time-of-flight, structured light, stereo image,or the like. According to one embodiment, the capture device 20 mayorganize the depth information into “Z layers,” or layers that may beperpendicular to a Z axis extending from the depth camera along its lineof sight.

As shown in FIG. 2, the capture device 20 may include an image cameracomponent 22. According to an example embodiment, the image cameracomponent 22 may be a depth camera that may capture the depth image of ascene. The depth image may include a two-dimensional (2-D) pixel area ofthe captured scene where each pixel in the 2-D pixel area may representa depth value such as a length or distance in, for example, centimeters,millimeters, or the like of an object in the captured scene from thecamera.

As shown in FIG. 2, according to an example embodiment, the image cameracomponent 22 may include an IR light component 24, a three-dimensional(3-D) camera 26, and an RGB camera 28 that may be used to capture thedepth image of a scene. For example, in time-of-flight analysis, the IRlight component 24 of the capture device 20 may emit an infrared lightonto the scene and may then use sensors (not shown) to detect thebackscattered light from the surface of one or more targets and objectsin the scene using, for example, the 3-D camera 26 and/or the RGB camera28. In some embodiments, pulsed infrared light may be used such that thetime between an outgoing light pulse and a corresponding incoming lightpulse may be measured and used to determine a physical distance from thecapture device 20 to a particular location on the targets or objects inthe scene. Additionally, in other example embodiments, the phase of theoutgoing light wave may be compared to the phase of the incoming lightwave to determine a phase shift. The phase shift may then be used todetermine a physical distance from the capture device to a particularlocation on the targets or objects.

According to another example embodiment, time-of-flight analysis may beused to indirectly determine a physical distance from the capture device20 to a particular location on the targets or objects by analyzing theintensity of the reflected beam of light over time via varioustechniques including, for example, shuttered light pulse imaging.

In another example embodiment, the capture device 20 may use astructured light to capture depth information. In such an analysis,patterned light (i.e., light displayed as a known pattern such as gridpattern or a stripe pattern) may be projected onto the scene via, forexample, the IR light component 24. Upon striking the surface of one ormore targets or objects in the scene, the pattern may become deformed inresponse. Such a deformation of the pattern may be captured by, forexample, the 3-D camera 26 and/or the RGB camera 28 and may then beanalyzed to determine a physical distance from the capture device to aparticular location on the targets or objects.

According to another embodiment, the capture device 20 may include twoor more physically separated cameras that may view a scene fromdifferent angles to obtain visual stereo data that may be resolved togenerate depth information.

The capture device 20 may further include a microphone 30. Themicrophone 30 may include a transducer or sensor that may receive andconvert sound into an electrical signal. According to one embodiment,the microphone 30 may be used to reduce feedback between the capturedevice 20 and the computing environment 12 in the target recognition,analysis, and tracking system 10. Additionally, the microphone 30 may beused to receive audio signals that may also be provided by the user tocontrol applications such as game applications, non-game applications,or the like that may be executed by the computing environment 12.

In an example embodiment, the capture device 20 may further include aprocessor 32 that may be in operative communication with the imagecamera component 22. The processor 32 may include a standardizedprocessor, a specialized processor, a microprocessor, or the like thatmay execute instructions including, for example, instructions forreceiving a depth image; generating a grid of voxels based on the depthimage; determining whether one or more voxels in the grid are associatedwith a background; discarding the one or more voxels associated with thebackground to isolate voxels associated with a foreground object in thedepth image; processing the grid with the isolated foreground object, orany other suitable instruction, which will be described in more detailbelow.

The capture device 20 may further include a memory component 34 that maystore the instructions that may be executed by the processor 32, imagesor frames of images captured by the 3-D camera or RGB camera, or anyother suitable information, images, or the like. According to an exampleembodiment, the memory component 34 may include random access memory(RAM), read only memory (ROM), cache, Flash memory, a hard disk, or anyother suitable storage component. As shown in FIG. 2, in one embodiment,the memory component 34 may be a separate component in communicationwith the image capture component 22 and the processor 32. According toanother embodiment, the memory component 34 may be integrated into theprocessor 32 and/or the image capture component 22.

As shown in FIG. 2, the capture device 20 may be in communication withthe computing environment 12 via a communication link 36. Thecommunication link 36 may be a wired connection including, for example,a USB connection, a Firewire connection, an Ethernet cable connection,or the like and/or a wireless connection such as a wireless 802.11b, g,a, or n connection. According to one embodiment, the computingenvironment 12 may provide a clock to the capture device 20 that may beused to determine when to capture, for example, a scene via thecommunication link 36.

Additionally, the capture device 20 may provide the depth informationand images captured by, for example, the 3-D camera 26 and/or the RGBcamera 28, and/or a skeletal model that may be generated by the capturedevice 20 to the computing environment 12 via the communication link 36.The computing environment 12 may then use the model, depth information,and captured images to, for example, control an application such as agame or word processor and/or animate an avatar or on-screen character.For example, as shown, in FIG. 2, the computing environment 12 mayinclude a gestures library 190. The gestures library 190 may include acollection of gesture filters, each comprising information concerning agesture that may be performed by the skeletal model (as the user moves).The data captured by the cameras 26, 28 and the capture device 20 in theform of the skeletal model and movements associated with it may becompared to the gesture filters in the gesture library 190 to identifywhen a user (as represented by the skeletal model) has performed one ormore gestures. Those gestures may be associated with various controls ofan application. Thus, the computing environment 12 may use the gestureslibrary 190 to interpret movements of the skeletal model and to controlan application based on the movements.

FIG. 3 illustrates an example embodiment of a computing environment thatmay be used to interpret one or more gestures in a target recognition,analysis, and tracking system and/or animate an avatar or on-screencharacter displayed by the target recognition, analysis, and trackingsystem. The computing environment such as the computing environment 12described above with respect to FIGS. 1A-2 may be a multimedia console100, such as a gaming console. As shown in FIG. 3, the multimediaconsole 100 has a central processing unit (CPU) 101 having a level 1cache 102, a level 2 cache 104, and a flash ROM (Read Only Memory) 106.The level 1 cache 102 and a level 2 cache 104 temporarily store data andhence reduce the number of memory access cycles, thereby improvingprocessing speed and throughput. The CPU 101 may be provided having morethan one core, and thus, additional level 1 and level 2 caches 102 and104. The flash ROM 106 may store executable code that is loaded duringan initial phase of a boot process when the multimedia console 100 ispowered ON.

A graphics processing unit (GPU) 108 and a video encoder/video codec(coder/decoder) 114 form a video processing pipeline for high speed andhigh resolution graphics processing. Data is carried from the graphicsprocessing unit 108 to the video encoder/video codec 114 via a bus. Thevideo processing pipeline outputs data to an A/V (audio/video) port 140for transmission to a television or other display. A memory controller110 is connected to the GPU 108 to facilitate processor access tovarious types of memory 112, such as, but not limited to, a RAM (RandomAccess Memory).

The multimedia console 100 includes an I/O controller 120, a systemmanagement controller 122, an audio processing unit 123, a networkinterface controller 124, a first USB host controller 126, a second USBcontroller 128 and a front panel I/O subassembly 130 that are preferablyimplemented on a module 118. The USB controllers 126 and 128 serve ashosts for peripheral controllers 142(1)-142(2), a wireless adapter 148,and an external memory device 146 (e.g., flash memory, external CD/DVDROM drive, removable media, etc.). The network interface 124 and/orwireless adapter 148 provide access to a network (e.g., the Internet,home network, etc.) and may be any of a wide variety of various wired orwireless adapter components including an Ethernet card, a modem, aBluetooth module, a cable modem, and the like.

System memory 143 is provided to store application data that is loadedduring the boot process. A media drive 144 is provided and may comprisea DVD/CD drive, hard drive, or other removable media drive, etc. Themedia drive 144 may be internal or external to the multimedia console100. Application data may be accessed via the media drive 144 forexecution, playback, etc. by the multimedia console 100. The media drive144 is connected to the I/O controller 120 via a bus, such as a SerialATA bus or other high speed connection (e.g., IEEE 1394).

The system management controller 122 provides a variety of servicefunctions related to assuring availability of the multimedia console100. The audio processing unit 123 and an audio codec 132 form acorresponding audio processing pipeline with high fidelity and stereoprocessing. Audio data is carried between the audio processing unit 123and the audio codec 132 via a communication link. The audio processingpipeline outputs data to the A/V port 140 for reproduction by anexternal audio player or device having audio capabilities.

The front panel I/O subassembly 130 supports the functionality of thepower button 150 and the eject button 152, as well as any LEDs (lightemitting diodes) or other indicators exposed on the outer surface of themultimedia console 100. A system power supply module 136 provides powerto the components of the multimedia console 100. A fan 138 cools thecircuitry within the multimedia console 100.

The CPU 101, GPU 108, memory controller 110, and various othercomponents within the multimedia console 100 are interconnected via oneor more buses, including serial and parallel buses, a memory bus, aperipheral bus, and a processor or local bus using any of a variety ofbus architectures. By way of example, such architectures can include aPeripheral Component Interconnects (PCI) bus, PCI-Express bus, etc.

When the multimedia console 100 is powered ON, application data may beloaded from the system memory 143 into memory 112 and/or caches 102, 104and executed on the CPU 101. The application may present a graphicaluser interface that provides a consistent user experience whennavigating to different media types available on the multimedia console100. In operation, applications and/or other media contained within themedia drive 144 may be launched or played from the media drive 144 toprovide additional functionalities to the multimedia console 100.

The multimedia console 100 may be operated as a standalone system bysimply connecting the system to a television or other display. In thisstandalone mode, the multimedia console 100 allows one or more users tointeract with the system, watch movies, or listen to music. However,with the integration of broadband connectivity made available throughthe network interface 124 or the wireless adapter 148, the multimediaconsole 100 may further be operated as a participant in a larger networkcommunity.

When the multimedia console 100 is powered ON, a set amount of hardwareresources are reserved for system use by the multimedia consoleoperating system. These resources may include a reservation of memory(e.g., 16 MB), CPU and GPU cycles (e.g., 5%), networking bandwidth(e.g., 8 kbs), etc. Because these resources are reserved at system boottime, the reserved resources do not exist from the application's view.

In particular, the memory reservation preferably is large enough tocontain the launch kernel, concurrent system applications and drivers.The CPU reservation is preferably constant such that if the reserved CPUusage is not used by the system applications, an idle thread willconsume any unused cycles.

With regard to the GPU reservation, lightweight messages generated bythe system applications (e.g., popups) are displayed by using a GPUinterrupt to schedule code to render popup into an overlay. The amountof memory required for an overlay depends on the overlay area size andthe overlay preferably scales with screen resolution. Where a full userinterface is used by the concurrent system application, it is preferableto use a resolution independent of application resolution. A scaler maybe used to set this resolution such that the need to change frequencyand cause a TV resynch is eliminated.

After the multimedia console 100 boots and system resources arereserved, concurrent system applications execute to provide systemfunctionalities. The system functionalities are encapsulated in a set ofsystem applications that execute within the reserved system resourcesdescribed above. The operating system kernel identifies threads that aresystem application threads versus gaming application threads. The systemapplications are preferably scheduled to run on the CPU 101 atpredetermined times and intervals in order to provide a consistentsystem resource view to the application. The scheduling is to minimizecache disruption for the gaming application running on the console.

When a concurrent system application requires audio, audio processing isscheduled asynchronously to the gaming application due to timesensitivity. A multimedia console application manager (described below)controls the gaming application audio level (e.g., mute, attenuate) whensystem applications are active.

Input devices (e.g., controllers 142(1) and 142(2)) are shared by gamingapplications and system applications. The input devices are not reservedresources, but are to be switched between system applications and thegaming application such that each will have a focus of the device. Theapplication manager preferably controls the switching of input stream,without knowledge the gaming application's knowledge and a drivermaintains state information regarding focus switches. The cameras 26, 28and capture device 20 may define additional input devices for theconsole 100.

FIG. 4 illustrates another example embodiment of a computing environment220 that may be the computing environment 12 shown in FIGS. 1A-2 used tointerpret one or more gestures in a target recognition, analysis, andtracking system and/or animate an avatar or on-screen characterdisplayed by a target recognition, analysis, and tracking system. Thecomputing system environment 220 is only one example of a suitablecomputing environment and is not intended to suggest any limitation asto the scope of use or functionality of the presently disclosed subjectmatter. Neither should the computing environment 220 be interpreted ashaving any dependency or requirement relating to any one or combinationof components illustrated in the exemplary operating environment 220. Insome embodiments the various depicted computing elements may includecircuitry configured to instantiate specific aspects of the presentdisclosure. For example, the term circuitry used in the disclosure caninclude specialized hardware components configured to performfunction(s) by firmware or switches. In other examples embodiments theterm circuitry can include a general purpose processing unit, memory,etc., configured by software instructions that embody logic operable toperform function(s). In example embodiments where circuitry includes acombination of hardware and software, an implementer may write sourcecode embodying logic and the source code can be compiled into machinereadable code that can be processed by the general purpose processingunit. Since one skilled in the art can appreciate that the state of theart has evolved to a point where there is little difference betweenhardware, software, or a combination of hardware/software, the selectionof hardware versus software to effectuate specific functions is a designchoice left to an implementer. More specifically, one of skill in theart can appreciate that a software process can be transformed into anequivalent hardware structure, and a hardware structure can itself betransformed into an equivalent software process. Thus, the selection ofa hardware implementation versus a software implementation is one ofdesign choice and left to the implementer.

In FIG. 4, the computing environment 220 comprises a computer 241, whichtypically includes a variety of computer readable media. Computerreadable media can be any available media that can be accessed bycomputer 241 and includes both volatile and nonvolatile media, removableand non-removable media. The system memory 222 includes computer storagemedia in the form of volatile and/or nonvolatile memory such as readonly memory (ROM) 223 and random access memory (RAM) 260. A basicinput/output system 224 (BIOS), containing the basic routines that helpto transfer information between elements within computer 241, such asduring start-up, is typically stored in ROM 223. RAM 260 typicallycontains data and/or program modules that are immediately accessible toand/or presently being operated on by processing unit 259. By way ofexample, and not limitation, FIG. 4 illustrates operating system 225,application programs 226, other program modules 227, and program data228.

The computer 241 may also include other removable/non-removable,volatile/nonvolatile computer storage media. By way of example only,FIG. 4 illustrates a hard disk drive 238 that reads from or writes tonon-removable, nonvolatile magnetic media, a magnetic disk drive 239that reads from or writes to a removable, nonvolatile magnetic disk 254,and an optical disk drive 240 that reads from or writes to a removable,nonvolatile optical disk 253 such as a CD ROM or other optical media.Other removable/non-removable, volatile/nonvolatile computer storagemedia that can be used in the exemplary operating environment include,but are not limited to, magnetic tape cassettes, flash memory cards,digital versatile disks, digital video tape, solid state RAM, solidstate ROM, and the like. The hard disk drive 238 is typically connectedto the system bus 221 through an non-removable memory interface such asinterface 234, and magnetic disk drive 239 and optical disk drive 240are typically connected to the system bus 221 by a removable memoryinterface, such as interface 235.

The drives and their associated computer storage media discussed aboveand illustrated in FIG. 4, provide storage of computer readableinstructions, data structures, program modules and other data for thecomputer 241. In FIG. 4, for example, hard disk drive 238 is illustratedas storing operating system 258, application programs 257, other programmodules 256, and program data 255. Note that these components can eitherbe the same as or different from operating system 225, applicationprograms 226, other program modules 227, and program data 228. Operatingsystem 258, application programs 257, other program modules 256, andprogram data 255 are given different numbers here to illustrate that, ata minimum, they are different copies. A user may enter commands andinformation into the computer 241 through input devices such as akeyboard 251 and pointing device 252, commonly referred to as a mouse,trackball or touch pad. Other input devices (not shown) may include amicrophone, joystick, game pad, satellite dish, scanner, or the like.These and other input devices are often connected to the processing unit259 through a user input interface 236 that is coupled to the systembus, but may be connected by other interface and bus structures, such asa parallel port, game port or a universal serial bus (USB). The cameras26, 28 and capture device 20 may define additional input devices for theconsole 100. A monitor 242 or other type of display device is alsoconnected to the system bus 221 via an interface, such as a videointerface 232. In addition to the monitor, computers may also includeother peripheral output devices such as speakers 244 and printer 243,which may be connected through a output peripheral interface 233.

The computer 241 may operate in a networked environment using logicalconnections to one or more remote computers, such as a remote computer246. The remote computer 246 may be a personal computer, a server, arouter, a network PC, a peer device or other common network node, andtypically includes many or all of the elements described above relativeto the computer 241, although only a memory storage device 247 has beenillustrated in FIG. 4. The logical connections depicted in FIG. 2include a local area network (LAN) 245 and a wide area network (WAN)249, but may also include other networks. Such networking environmentsare commonplace in offices, enterprise-wide computer networks, intranetsand the Internet.

When used in a LAN networking environment, the computer 241 is connectedto the LAN 245 through a network interface or adapter 237. When used ina WAN networking environment, the computer 241 typically includes amodem 250 or other means for establishing communications over the WAN249, such as the Internet. The modem 250, which may be internal orexternal, may be connected to the system bus 221 via the user inputinterface 236, or other appropriate mechanism. In a networkedenvironment, program modules depicted relative to the computer 241, orportions thereof, may be stored in the remote memory storage device. Byway of example, and not limitation, FIG. 4 illustrates remoteapplication programs 248 as residing on memory device 247. It will beappreciated that the network connections shown are exemplary and othermeans of establishing a communications link between the computers may beused.

FIG. 5 depicts a flow diagram of an example method 300 for processingdepth information a scene. The example method 300 may be implementedusing, for example, the capture device 20 and/or the computingenvironment 12 of the target recognition, analysis, and tracking system10 described with respect to FIGS. 1A-4. In an example embodiment, theexample method 300 may take the form of program code (i.e.,instructions) that may be executed by, for example, the capture device20 and/or the computing environment 12 of the target recognition,analysis, and tracking system 10 described with respect to FIGS. 1A-4.

According to one embodiment, at 305, a depth image may be received. Forexample, the target recognition, analysis, and tracking system mayinclude a capture device such as the capture device 20 described abovewith respect to FIGS. 1A-2. The capture device may capture or observe ascene that may include one or more targets. In an example embodiment,the capture device may be a depth camera configured to obtain an imagesuch as an a depth image of the scene using any suitable technique suchas time-of-flight analysis, structured light analysis, stereo visionanalysis, or the like.

The depth image may be a plurality of observed pixels where eachobserved pixel has an observed depth value. For example, the depth imagemay include a two-dimensional (2-D) pixel area of the captured scenewhere each pixel in the 2-D pixel area may have a depth value such as alength or distance in, for example, centimeters, millimeters, or thelike of an object in the captured scene from the capture device.

FIG. 6 illustrates an example embodiment of a depth image 400 that maybe received at 305. According to an example embodiment, the depth image400 may be an image or frame of a scene captured by, for example, the3-D camera 26 and/or the RGB camera 28 of the capture device 20described above with respect to FIG. 2. As shown in FIG. 6, the depthimage 400 may include a human target 402 a corresponding to, forexample, a user such as the user 18 described above with respect toFIGS. 1A and 1B and one or more non-human targets 404 such as a wall, atable, a monitor, or the like in the captured scene. As described above,the depth image 400 may include a plurality of observed pixels whereeach observed pixel has an observed depth value associated therewith.For example, the depth image 400 may include a two-dimensional (2-D)pixel area of the captured scene where each pixel at particular X-valueand Y-value in the 2-D pixel area may have a depth value such as alength or distance in, for example, centimeters, millimeters, or thelike of a target or object in the captured scene from the capturedevice.

In one embodiment, the depth image 400 may be colorized such thatdifferent colors of the pixels of the depth image correspond to and/orvisually depict different distances of the human target 402 a andnon-human targets 404 from the capture device. For example, the pixelsassociated with a target closest to the capture device may be coloredwith shades of red and/or orange in the depth image whereas the pixelsassociated with a target further away may be colored with shades ofgreen and/or blue in the depth image.

Referring back to FIG. 5, in one embodiment, upon receiving the image,at 305, one or more high-variance and/or noisy depth values may beremoved and/or smoothed from the depth image; portions of missing and/orremoved depth information may be filled in and/or reconstructed; and/orany other suitable processing may be performed on the received depthimage may such that the depth information associated with the depthimage may be used to generate a model such as a skeletal model, whichwill be described in more detail below.

According to an example embodiment, at 310, a grid of one or more voxelsmay be generated based on the received depth image. For example, thetarget recognition, analysis, and tracking system may downsample thereceived depth image by generating one or more voxels using informationincluded in the received depth image such that a downsampled depth imagemay be generated. In one embodiment, the one or more voxels may bevolume elements that may represent data or values of the informationincluded in the received depth image on a sub-sampled grid.

For example, as described above, the depth image may include a 2-D pixelarea of the captured scene where each pixel may have an X-value, aY-value, and a depth value (or Z-value) associated therewith. In oneembodiment, the depth image may be downsampled by reducing the pixels inthe 2-D pixel area into a grid of one or more voxels. For example, thedepth image may be divided into portions or blocks of pixels such as 4×4blocks of pixels, 5×5 blocks of pixels, 8×8 blocks of pixels, a 10×10block of pixels, or the like. Each portion or block may be processed togenerate a voxel for the depth image that may represent a position ofthe portion or block associated the pixels of the 2-D depth image inreal-world space. According to an example embodiment, the position ofeach voxel may be generated based on, for example, an average depthvalue of the valid or non-zero depth values for the pixels in the blockor portion that the voxel may represent, a minimum and/or maximum depthvalue of the pixels in the portion or block that the voxel mayrepresent, an average of the X-values and Y-values for pixels having avalid depth value in the portion or the block that the voxel mayrepresent, or any other suitable information provided by the depthimage. Thus, according to an example embodiment, each voxel mayrepresent a sub-volume portion or block of the depth image having valuessuch as an average depth value of the valid or non-zero depth values forthe pixels in the block or portion that the voxel may represent, aminimum and/or maximum depth value of the pixels in the portion or blockthat the voxel may represent, an average of the X-values and Y-valuesfor pixels having a valid depth value in the portion or the block thatthe voxel may represent, or any other suitable information provided bythe depth imagebased on the X-values, Y-values, and depth values of thecorresponding portion or block of pixels of the depth image received at305.

In one embodiment, the grid of the one or more voxels in the downsampleddepth image may be layered. For example, the target recognition,analysis, and tracking system may generate voxels as described above.The target recognition, analysis, and tracking system may then stack agenerated voxel over one or more other generated voxels in the grid.

According to an example embodiment, the target recognition, analysis,and tracking system may stack voxels in the grid around, for example,edges of objects in the scene that may be captured in the depth image.For example, a depth image received at 305 may include a human targetand a non-human target such as a wall. The human target may overlap thenon-human target such as the wall at, for example, an an edge of thehuman target. In one embodiment, the overlapping edge may includeinformation such as depth values, X-values, Y-values values, or the likeassociated with the human target and the non-human target that may becaptured in the depth image. The target recognition, analysis, andtracking system may generate a voxel associated with the human targetand a voxel associated with the non-human target at the overlapping edgesuch that the voxels may be stacked and the information such as depthvalues, X-values, Y-values, or the like of the overlapping edge may beretained in the grid.

According to another embodiment, the grid of one or more voxels may begenerated at 310 by projecting, for example, information such as thedepth values, X-values, Y-values, or the like for the pixels in thedepth image that may be received at 305 into a three-dimensional (3-D)space. For example, the target recognition, analysis, and trackingsystem may map information such as the depth values, X-values, Y-values,or the like for the pixels in the depth image to 3-D points in the 3-Dspace using a transformation such as a camera, image, or perspectivetransform such that the information may be transformed as trapezoidal orpyramidal shapes in the 3-D space. In one embodiment, the 3-D spacehaving the trapezoidal or pyramidal shapes may be divided into blockssuch as cubes that may create a grid of voxels such that each of theblocks or cubes may represent a voxel in the grid. For example, thetarget recognition, analysis, and tracking system may superimpose a 3-Dgrid over the 3-D points that correspond to the object in the depthimage. The target recognition, analysis, and tracking system may thendivide or chop up the grid into the blocks representing voxels todownsample the depth image into a lower resolution. According to anexample embodiment, each of the voxels in the grid may include anaverage depth value of the valid or non-zero depth values for the pixelsassociated with the 3-D space in the grid that the voxel may represent,a minimum and/or maximum depth value of the pixels associated with the3-D space in the grid that the voxel may represent, an average of theX-values and Y-values for pixels having a valid depth value associatedwith the 3-D space in the grid that the voxel may represent, or anyother suitable information provided by the depth image.

FIGS. 7A-7B illustrates an example embodiment of a portion of the depthimage being downsampled. For example, as shown in FIG. 7A, a portion 410of the depth image 400 described above with respect to FIG. 6 mayinclude a plurality of pixels 420 where each pixel 420 may have anX-value, a Y-value, and a depth value (or Z-value) associated therewith.. According to one embodiment, as described above, a depth image such asthe depth image 400 may be downsampled by reducing the pixels in the 2-Dpixel area into a grid of one or more voxels. For example, as shown inFIGS. 7A, the portion 410 of the depth image 400 may be divided into aportion or a block 430 of the pixels 420 such as 8×8 block of the pixels420. The target recognition, analysis, and tracking system may processthe portion or block 430 to generate a voxel 440 that may represent aposition of the portion or block 430 associated the pixels 420 inreal-world space as shown in FIGS. 7A-7B.

Referring back to FIG. 5, at 315, a background of the grid of voxelsincluded in the downsampled depth image may be determined. For example,a background such as the non-human targets or objects in the downsampleddepth image may be determined such that the background may be removed ordiscarded to isolate foreground objects such as a human targetassociated with a user, which will be described in more detail below. Inone embodiment, as described above, the target recognition, analysis,and tracking system may downsample a captured or observed depth image bygenerating a grid of one or more voxels for the captured or observeddepth image. The target recognition, analysis, and tracking system mayanalyze each of the voxels in the downsampled depth image to determinewhether a voxel may be associated with a background object such as oneor more non-human targets of the depth image. If a voxel may beassociated with a background object, the voxel may be removed ordiscarded from the downsampled depth image such that a foreground objectsuch as the human target and the one or more voxels in the gridassociated with the foreground object may be isolated, which will bedescribed in more detail below.

According to one embodiment, the target recognition, analysis, andtracking system may analyze each voxel to determine an object associatedtherewith. For example, as described above, a scene that may be observedor captured at 305 as a depth image such as the depth image 400described above with respect to FIG. 6 may include a plurality ofobjects. The objects may include one or more human targets and/or one ormore non-human targets such as a wall, a table, a couch, a lamp, or thelike. In one embodiment, the target, recognition, analysis, and trackingsystem may analyze each voxel in the grid to determine which object inthe scene the voxel may be as associated with such that the targetrecognition, analysis, and tracking system may identify voxelsassociated with each object in a scene at 315. Thus, according to anexample embodiment, if a human target or person may be standing in frontof a wall in a scene, the target recognition, analysis, and trackingsystem may analyze each voxel to determine whether the voxel may beassociated with the human target or the wall.

To determine which object in the scene a voxel may be associated with,the target, recognition, analysis, and tracking system may comparevalues such as an average depth value of the valid or non-zero depthvalues for the pixels in the block or portion that the voxel mayrepresent, a minimum and/or maximum depth value of the pixels in theportion or block that the voxel may represent, an average of the Xvalues and Y values for pixels having a valid depth value that the voxelmay represent, or any other suitable information of neighboring ornearby voxels. For example, in one embodiment, the minimum depth valueassociated with a particular voxel being analyzed in the grid maycompared to the minimum depth values of each voxel that may be adjacentto the particular voxel being analyzed in the grid. If the differencebetween the minimum depth value of the particular voxel being analyzedand a minimum depth value of an adjacent voxel may be less than athreshold, the particular voxel and the adjacent voxel may be identifiedas belonging to the same object. If the difference between the minimumdepth value of the particular voxel being analyzed and an minimum depthvalue of an adjacent voxel may be greater than the threshold, theparticular voxel and the adjacent voxel may be identified as belongingto separate objects. According to an example embodiment, the thresholdmay be a predetermined value generated by, for example, the targetrecognition, analysis, and tracking system that may be based on alikelihood or probability that voxels may be part of the same object.Thus, according to an example embodiment, if a human target or personmay be standing in front of a wall in a scene captured or observed bythe depth image, the target recognition, analysis, and tracking systemmay analyze each voxel generated for the depth image to determinewhether the voxel may be associated with the human target or the wall.

After identifying the objects and the voxels associated therewith in thescene of the received depth image, the target recognition, analysis, andtracking system may then calculate information associated with eachidentified object. For example, the target recognition, analysis, andtracking system may calculate a maximum world space for each identifiedobject, a minimum world space position, and an average world spaceposition, or the like.

In one embodiment, the target recognition, analysis, and tracking systemmay further determine whether one or more of the objects identified in ascene should be merged with other objects in the scene at 315. Forexample, part or a portion of an object may be separated from anotherpart or portion of the object in the depth image received at 305.According to one embodiment, the part or portion of an object may beseparated from another part or portion of the object by an infraredshadow that may be cast by, for example, the object, another object, orthe like in the scene. In another example embodiment, the part orportion of an object may be separated from another part or portion ofthe object by, for example, colors, textures, patterns, or the likeassociated with the object. For example, a head of a human target may beseparated from a torso of the human target along an Y-plane in theY-direction by, for example, facial hair, various articles of clothing,or the like.

To determine whether an object identified in the scene may actually be apart or a portion of another object identified in the scene, the targetrecognition, analysis, and tracking system may compare the X-values,Y-values, and/or the depth values of the voxels associated with theobject with X-values, Y-values, and/or depth values of the voxelsassociated with nearby objects. For example, the target recognition,analysis, and tracking system may compare an X-value, a Y-value and/or adepth value of one or more voxels associated with, for example, a firstobject identified in the scene with an X-value, a Y-value, and/or adepth value of one or more voxels associated with a second object thatmay be nearby or adjacent to the first object. Thus, according to anexample embodiment, the target recognition, analysis, and trackingsystem may analyze the voxels in a scene to determine whether a firstand second object may overlap along the X-plane defined in theX-direction, the Y-plane defined in the Y-direction, and/or the Z-planedefined in the Z-direction such that the first and second objects may bemerged and identified as being parts or portions of the same object.

According to one embodiment, if the X-value, the Y-value, and/or thedepth value of one or more voxels associated with the first object mayoverlap an X-value, a Y-value and/or a depth value of one or more voxelsassociated with the second object, the target recognition, analysis, andtracking system may merge the first and second objects such that thetarget recognition, analysis, and tracking system may identify the firstand second objects as being parts or portions of a common object. Forexample, if a first voxel associated with a first object may have anX-value of 5 along the X-direction and a depth value of 10 mm at a rightouter edge of the first object and a second voxel associated with asecond object may have an X-value of 3 along the X-direction and a depthvalue of 10 mm at a left outer edge of the second object, the targetrecognition, analysis, and target system may determine that the firstand second objects may overlap. The target, recognition, analysis, andtracking system may then merge the first and second objects such thatthe target, recognition, analysis, and tracking system may identify thefirst and second objects as being parts or portions of the same object.

Additionally, to determine whether an object identified in the scene mayactually be a part or a portion of another object identified in thescene, the target recognition, analysis, and tracking system maydetermine whether a bounding box defined for an object overlaps abounding box of another object in the scene. For example, the targetrecognition, analysis, and tracking system may define a bounding box foreach identified object. The target recognition, analysis, and trackingsystem may then determine whether the bounding boxes of one or moreobjects overlap based on, for example, X-values, Y-values, and/or depthvalues of one or more voxels included therein as described above.

According to another example, embodiment, the target recognition,analysis, and tracking system may determine a center or centroid of eachobject by, for example, averaging the X-values, Y-values, and depthvalues of the voxels included in the object. The target recognition,analysis, and tracking system may then determine a distance between thecentroid or center of objects in the scene to determine whether anobject identified in the scene may actually be a part or a portion ofanother object identified in the scene. Based on the distance betweenobjects, the target, recognition, analysis, and tracking system maymerge one or more objects. For example, the target recognition,analysis, and tracking system may determine a distance between acentroid or center of a first object and a center or centroid of asecond object. If the distance between the centroid or center of thefirst object and the second object may be within a predetermined rangethat indicates the first and second objects should be merged, the targetrecognition, analysis, and tracking system may merge the objects suchthat the target, recognition, analysis, and tracking system may identifythe first and second objects as being parts or portions of the sameobject.

In one embodiment, the target recognition, analysis, and tracking systemmay further determine whether one or more of the objects identified inthe scene should be separated at 315. For example, an object identifiedin the scene at 315 may actually be two separate objects. To determinewhether an object in the scene should be separated, the targetrecognition, analysis, and tracking system may identify a location of acenter of each object determined for a previously received frame.According to one embodiment, the target recognition, analysis, andtracking system may then simultaneously floodfill the voxels in thescene generated for the depth image of the frame received at 305starting with the location of the center determined from the objects ofthe previously received frame. The target recognition, analysis, andtracking system may then determine which object in the previouslyreceived frame the floodfilled voxels may be closer to using theprevious locations for the objects. The target recognition, analysis,and tracking system may split an object at 315 if the floodfilled voxelsmay be closer to another object identified in a previously receivedframe.

At 315, the target recognition, analysis, and tracking system mayfurther determine whether the identified objects may be a backgroundobject such as non-human target or a foreground object such as a humantarget. According to an example embodiment, the target recognition,analysis, and tracking system may determine whether the identifiedobjects may be a background object or a foreground object based onwhether the identified objects may be in motion or moving. For example,the target recognition, analysis, and tracking system may include areference plate such as a reference image of the scene that includes,for example, non-motion depth information for each voxel. According toone embodiment, the reference plate may include a moving averageassociated with each voxel in the scene. The moving average may include,for example, an average depth value of a voxel determined over a seriesof previously received frames.

In other example embodiments, the reference plate may also include aminimum world space position of the voxels such as the minimum X-values,Y-values, and depth values for the voxels in the grid determined over aseries of previously received frames, a maximum world space position ofthe voxels such as the maximum X-values, Y-values, and depth values forthe voxels in the grid determined over a series of previously receivedframes, an average world position of the voxels such as the averageX-values, Y-values, and depth values for the voxels in the griddetermined over a series of previously received frames, or any othersuitable reference plate.

According to one embodiment, the target recognition, analysis, andtracking system may compare depth information such as a maximum depthvalue, an average depth value, a minimum depth value, or the like ofeach voxel associated with the identified objects in the scene of thedepth image received at, for example, 305 with the non-motion depthinformation of each corresponding voxel included in the reference plate.Based on the comparison of the depth information and the non-motiondepth information of the corresponding voxel in the reference plate, thetarget recognition, analysis, and tracking system may identify a voxelas moving. For example, in one embodiment, if a depth value such as theminimum depth value, the maximum depth value, and/or the average depthvalue of a voxel may be less than the moving average of thecorresponding voxel in the reference plate such that the voxel may be infront of the moving average, the voxel may be identified as moving.According to another example embodiment, the target recognition,analysis, and tracking system may calculate a difference between thevalues associated with the voxel and the corresponding voxel in thereference plate. If, for example, a difference between a depth valuesuch as the average depth value, the maximum depth value, and/or theminimum depth value of a voxel and depth values included in thenon-motion information of the corresponding voxel in the reference platemay be greater than a motion threshold, the voxel may be identified bythe target recognition, analysis, and tracking system as moving.

In another example embodiment, the target recognition, analysis, andtracking system may compare depth information such as a maximum depthvalue, an average depth value, a minimum depth value, or the like of avoxel and the voxels adjacent thereto with the non-motion depthinformation of each corresponding voxel included in the reference plate.For example, to handle edge noise, the target recognition, analysis, andtracking system may compare a minimum depth value of a particular voxeland the voxels that may be adjacent thereto against the correspondingvoxel in the reference plate to determine whether a voxel and/or theobject associated therewith may be moving. If, for example, a differencebetween the minimum depth value of the particular voxel and the voxelsthat may be adjacent thereto and the minimum depth value included in thenon-motion information of the corresponding voxels in the referenceplate may be greater than a motion threshold, the particular voxel maybe identified by the target recognition, analysis, and tracking systemas moving.

The target recognition, analysis, and tracking system may then calculatea foreground score for each identified object based on a percentage ofmoving voxels. In one embodiment, the target recognition, analysis, andtracking system may divide the number of voxels included in the islandthat may be identified as moving by the total number of voxels includedin the island to calculate the foreground score.

At 320, the background may be removed or discarded. For example, asdescribed above. The target recognition, analysis, and tracking systemmay remove or discard the background to isolate a foreground object suchas a human target associated with a user. According to one embodiment,the target recognition, analysis, and tracking system may isolate theobject having a foreground score that may exceed a score threshold. Thescore threshold may be a value or percentage defined by the targetrecognition, analysis, and tracking system that may indicate an objectmay be in motion. For example, the target recognition, analysis, andtracking system may remove or discard the background objects that maynot be moving based on the foreground score from the downsampled depthimage such that the foreground object such as the human target that mayhave a foreground score that may exceed the score threshold may beisolated in the downsampled depth image.

Additionally, at 320, the target recognition, analysis, and trackingsystem may remove or discard the background objects and the voxelsassociated therewith based on a depth history. For example, the targetrecognition, analysis, and tracking system may include a reference platethat may include a depth history of the background object including, forexample, a minimum depth value and/or a maximum depth value for eachvoxel included in background objects captured over a series of frames.The target recognition, analysis, and tracking system may compare thevalues associated with a voxel such as X-values, Y-values, and depthvalues with the reference plate that may include the minimum depthvalues and/or the maximum depth value of the voxels associated with thebackground objects. Based on the comparison, the target recognition,analysis, and tracking system may determine whether a voxel may bebackground. For example, if the X-values, Y-values, or depth values of avoxel may be greater than, for example, a maximum depth value of acorresponding voxel in the reference plate, the target recognition,analysis, and tracking system may identify the voxel as being part ofthe background. The target, recognition, analysis, and tracking systemmay then remove or discard the voxel.

Thus, according to an example, the target recognition, analysis, andtracking system may determine whether a voxel may have a depth valueclose to or behind a depth value for a corresponding voxel in thereference plate that may include a depth history of the minimum ormaximum values observed for background objects. If the voxel may have adepth value close to or behind a depth value for a corresponding voxelin the reference plate, the target recognition, analysis, and trackingsystem may identify the voxel as being part of the background. Thetarget, recognition, analysis, and tracking system may then remove ordiscard the voxel.

According to an example embodiment, to remove or discard the objectsthat may not be moving and/or that may have a depth value close to orbehind a depth value in a reference plate that may include a depthhistory, the target recognition, analysis, and tracking system mayreplace the X-values, the Y-values, and/or the depth with a zero valueor another suitable indicator or flag that may indicate the voxel may beinvalid.

In one embodiment, after isolating the foreground object such as thehuman target, as described above, the target recognition, analysis, andtracking system may upsample the foreground object such that theforeground object may rendered in a higher resolution. For example, thetarget recognition, analysis, and tracking system may use the X-values,Y-values, and the depth values for the pixels that may be associatedwith the voxels of the foreground object to generate a higher resolutionforeground object.

The isolated voxels associated with the foreground object such as thehuman target may be processed at 325. In one embodiment, the targetrecognition, analysis, and tracking system may process the voxelsassociated with the isolated foreground object such as the human targetto determine a location or position of one or more extremities such as ahead, a centroid or center, shoulders, hips, arms, elbows, hands, legs,knees, feet, or the like. The target recognition, analysis, and trackingsystem may also process the voxels to determine dimensions such asmeasurements including widths, lengths, or the like of the one or moreextremities.

At 325, the target recognition, analysis, and tracking system may alsoprocess the voxels associated with the isolated foreground object suchthat a model of the foreground object such as the human target may begenerated. According to an example embodiment, the model may be trackedbased on the determined extremities and their dimensions, an avatarassociated with the model may be rendered and/or changed in response tochanges to the model being tracked, and/or one or more applicationsexecuting on a computer environment may be controlled.

It should be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered limiting. The specificroutines or methods described herein may represent one or more of anynumber of processing strategies. As such, various acts illustrated maybe performed in the sequence illustrated, in other sequences, inparallel, or the like. Likewise, the order of the above-describedprocesses may be changed.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

What is claimed:
 1. A computer-readable storage device having storedthereon computer executable instructions for processing depthinformation of a scene, the computer executable instructions comprisinginstructions for: receiving a depth image of the scene, wherein thedepth image comprises one or more objects; comparing a value associatedwith voxels in one or more objects in the depth image with acorresponding value of a reference voxel; identifying voxels as movingwhen a difference between the value and the corresponding value exceedsa motion threshold; and identifying other voxels as non-moving.
 2. Thecomputer-readable storage device of claim 1, the computer executableinstructions further comprising instructions for determining whether tomerge an object in the one or more objects with a nearby object in theone or more objects.
 3. The computer-readable storage device of claim 2,wherein determining whether to merge the object in the one or moreobjects with the nearby object in the one or more objects comprises:comparing X-values, Y-values, or depth values associated with voxels inthe object with X-values, Y-values, or depth values associated withvoxels of the nearby object; and merging the object with the nearbyobject if, based on the comparison, the X-values, Y-values, or the depthvalues associated with the voxels in the object overlap the X-values,Y-values, or depth values associated with the voxels of the nearbyobject.
 4. The computer-readable storage device of claim 1, the computerexecutable instructions further comprising instructions for: calculatinga foreground score based on a percentage of moving voxels associatedwith one of the objects; and identifying the one object as moving whenthe foreground score exceeds a score threshold.
 5. The computer-readablestorage device of claim 4, the computer executable instructions furthercomprising instructions for: isolating the one object associated withthe identified voxel that is moving; and processing the isolated object.6. The computer-readable storage device of claim 1, the computerexecutable instructions further comprising instructions for determiningthat at least one object of the one or more objects is non-moving. 7.The computer-readable storage device of claim 6, the computer executableinstructions further comprising instructions for discarding the at leastone non-moving object of the one or more objects.
 8. A system forprocessing depth information of a scene, the system comprising: acapture device configured to capture a depth image of the scene; and acomputing device communicatively coupled to the capture device, whereinthe computing device comprises a processor and memory storing thereoncomputer-readable instructions that, when executed by the processor,cause the computing device to perform operations comprising: receiving adepth image of the scene, wherein the depth image comprises one or moreobjects; comparing a value associated with voxels in one or more objectsin the depth image with a corresponding value of a reference voxel;identifying voxels as moving when a difference between the value and thecorresponding value exceeds a motion threshold; and identifying othervoxels as non-moving.
 9. The system of claim 8, further comprisingcomputer-readable instructions that, when executed by the processor,cause the computing device to perform operations comprising determiningwhether to merge an object in the one or more objects with a nearbyobject in the one or more objects.
 10. The system of claim 9, furthercomprising computer-readable instructions that, when executed by theprocessor, cause the computing device to perform operations comprising:determining whether merge an object in the one or more objects with anearby object in the one or more objects: comparing X-values or depthvalues associated with voxels in one of the object with X-values ordepth values associated with voxels of a nearby object; and merging theobject with the nearby object if, based on the comparison, the X-valuesor the depth values associated with the voxels in the object overlap theX-values or depth values associated with the voxels of the nearbyobject.
 11. The system of claim 9, further comprising computer-readableinstructions that, when executed by the processor, cause the computingdevice to perform operations comprising: calculating a foreground scorebased on a percentage of moving voxels associated with one of theobjects; and identifying the one object as moving when the foregroundscore exceeds a score threshold.
 12. The system of claim 11, furthercomprising computer-readable instructions that, when executed by theprocessor, cause the computing device to perform operations comprising:isolating the one object associated with the identified voxel that ismoving; and processing the isolated object.
 13. The system of claim 8,further comprising computer-readable instructions that, when executed bythe processor, cause the computing device to perform operationscomprising discarding at least one non-moving object of the one or moreobjects.
 14. A method for processing depth information of a scene, themethod comprising: receiving a depth image of the scene, wherein thedepth image comprises one or more objects; comparing a value associatedwith voxels in one or more objects in the depth image with acorresponding value of a reference voxel; identifying voxels as movingwhen a difference between the value and the corresponding value exceedsa motion threshold; and identifying other voxels as non-moving.
 15. Themethod of claim 14, further comprising determining whether to merge anobject in the one or more objects with a nearby object in the one ormore objects.
 16. The method of claim 15, wherein determining whether tomerge the object in the one or more objects with the nearby object inthe one or more objects comprises: comparing X-values, Y-values, ordepth values associated with voxels in the object with X-values,Y-values, or depth values associated with voxels of the nearby object;and merging the object with the nearby object if, based on thecomparison, the X-values, Y-values, or the depth values associated withthe voxels in the object overlap the X-values, Y-values, or depth valuesassociated with the voxels of the nearby object.
 17. The method of claim15, further comprising: calculating a foreground score based on apercentage of moving voxels associated with at least one object; andidentifying the at least one object as moving when the foreground scoreexceeds a score threshold.
 18. The method of claim 17, furthercomprising: isolating the at least one object associated with theidentified voxel that is moving; and processing the at least oneisolated object.
 19. The method of claim 14, further comprisingdetermining that at least one object of the one or more objects isnon-moving.
 20. The method of claim 19, further comprising discarding atleast one non-moving object of the one or more objects.